Field of Invention
The present invention relates to a semiconductor device.
Description of Related Art
As a form of a field effect transistor (FET), a high electron mobility transistor (HEMT) is widely used because of its high electron mobility and low resistance. A key element of the HEMT is a heterojunction formed by two materials with different band gaps, instead of a pn-junction used in the conventional FET. A commonly used material combination of the heterojunction is AlGaN and GaN. Since the heterojunction created by AlGaN and GaN forms a quantum well in the conduction band on the GaN side, a two-dimensional electron gas (2DEG) appears at the interface of AlGaN and GaN.